Photoelectric motor-speed foot controller



g- 1954 M.- R. BOSTRQM METAL 3,145,304

PHOTOELECTRIC MOTOR-SPEED BOOT CONTROLLER Filed May 21, 1962 Fig. 3

INVENTORS MARK R. BOSTROM AND WITNESS EDWARD W 72mm W BY 17 A ORNEY United States Patent 3,145,304 PHUTGELECTRHC MOTQR-SPEED FQGT CONTROLLER Mark R. Bostrom, Dover, and Edward W. Taylor, Martinsville, N..l., assignors to The Singer Company, a conporation of New Jersey Filed May 21, 1962, Ser. No. 196,390 1 Claim. (Cl. 253-239) This invention relates to foot controllers of the variable resistance type used to control the speed of electric motors for driving sewing machines and like devices.

Heretofore devices of this type have generally used wire-wound resistances with sliding contacts or compressible carbon piles. These prior devices have the disadvantage of generating considerable electrical noise causing interference with radio and television reception in their vicinity.

With the advent of circuits of the type illustrated by the United States patent application Serial No. 87,567, filed February 7, 1961, it becomes feasible to use low current variable resistance devices for handling the low gate currents of the silicon controlled rectifier which in turn controls the much higher motor current.

By using a photoconductive cell as the variable resistance element, it is possible to eliminate most of the radio-frequency interference of the prior art devices and still provide good speed control.

It is an object of this invention to provide a foot-controller of the variable resistance type having no sliding or pressure contacts in the electrical circuit. It is a further object of this invention to provide a footcontroller in which the entire resistance variation is obtained by controlling the amount of light transmission to a photoconductive element.

With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the invention and the advantages attained thereby will be readily understood by those skilled in the art.

In the drawing,

FIG. 1 is a typical section, partly in side elevation, through a device embodying the invention.

FIG. 2 is a sectional view, partly in top plan, taken through the device of FIG. 1.

FIG. 3 is an enlarged detail of a portion of the device of FIG. 1.

Referring to FIG. 1 a device embodying the invention is shown as comprising a base with a cover 11, both formed of opaque molded insulation material and providing an enclosure for the elements now to be described.

Secured to the base 10 by means of screws 12 is a bracket 13 having an upstanding arm 14 in which is slidably received a rod 15. A compression spring 16 embraces the rod between a headed portion 17 and the arm 14 to bias the rod to the right as viewed in FIG. 2. Secured to the rod 15 by opposed nuts 18 is a shutter blade 19 and a clevis 20.

A bell crank lever 21 is pivotally mounted on a pin 22 received in a saddle 23 formed in the base 10. A pin 24 pivotally connects the clevis to the bell crank lever 21 and a pedal element 25 slidable vertically through the cover 11 straddles a pin 26 to rock the bell crank lever 21 about the pin 22.

It will be seen from FIG. 1 that, when the pedal 25 is pushed down, the bell crank lever 21 rocks about pin 22 to the position shown in dotted lines. The clevis 20, rod

Patented Aug. 13, 1964 15 and shutter blade 19 are likewise moved against the bias of the spring 16 to the position shown in the dotted lines of FIG. 1.

A photoconductive cell 27 mounted in a socket 23 is positioned so as to be entirely covered by the shutter blade 19 in the normally biased condition of the parts as shown in FIG. 2. An opaque resilient sleeve 29 surrounds the cell 27 and forms with the shutter blade 19 a light-tight Wiping seal so that, in the fully-covered position shown by the dotted lines of FIG. 3, the cell 27 has its maximum resistance. As the pedal 25 is depressed, the shutter blade 19 moves to uncover the cell 27 until, in the fully depressed position, the blade 19 is in the positon indicated by the full lines of FIG. 3 thus exposing the full cell area and providing minimum cell resistance corresponding to maximum motor speed.

An exciter lamp 30, held in a clamp bracket 31 secured to the cover 11, is positioned directly above the cell 27 so that the shutter blade 19, by its movement, controls the amount of light transmitted from the lamp to the cell. The arrangement of the parts is such that the bracket 31 slidably contacts the shutter blade 19 with slight pressure to hold it in light-tight engagement with the sleeve 29, the blade 19 being sufliciently resilient to permit this function.

A small hole 32 in the cover 11 adjacent the cell 27 permits external indication that the controller is in operative condition.

Leads 33 from the cell 27 and leads 34 from the lamp 30 are formed into a four-conductor cable 35 for external connections.

A practical embodiment of this invention which has operated successfully uses a Sylvania Type lOESB indicator lamp operating from 10 volts, 6O cycle A.C. as the exciter lamp 30, and a North American Philips Company Cadmium Sulphide Cell Type LDR-Cl as the photoconductive cell 27. A General Electric Type NE-Z Neon lamp operating on US volts, 60 cycle AC. has also been used successfully as the exciter lamp 30.

While in the embodiment shown, the shutter blade 19 has a square-ended configuration, this invention is not to be construed as so limited but shall include within its scope shutter blades having any configuration, such as V-notches and serrated edges for example, which may be necessary for obtaining a desired characteristic of resistance versus pedal movement.

Having thus set forth the nature of this invention, what we claim herein is:

A photoelectric motor-speed controller comprising an opaque enclosure having a base and a cover, a photocell mounted on said base, a light source mounted on said cover adjacent to said photocell, a shutter mounted for movement between said light source and said photocell to variably control the amount of light transmission therebetWeen, an opaque resilient sleeve surrounding said photocell and forming with the movable shutter a light-tight wiping seal to minimize the effect of extraneous ambient light on the control characteristic, biasing means to normally position the shutter to cut oil all light transmission, and means including an external operator-influenced element for moving said shutter against said biasing means to efiect operator-controlled variable light transmission between the light source and the photocell.

References Cited in the file of this patent UNITED STATES PATENTS 2,832,259 Merton Apr. 29, 1958 3,046,831 lsreeli July 31, 1962 FOREIGN PATENTS 223,728 Australia July 14, 1959 

